In the processing of semiconductor wafers and other semiconductor pieces it is frequently necessary to expose surfaces of the semiconductor piece to chemicals. The chemicals can be reactants, coatings or solvents. In some processes the chemical activity is preferably limited to one side of the wafer or other semiconductor piece being processed. Limiting chemical activity to one side of a wafer is desirable in many liquid spray processes. Limiting chemical activity to one side of a wafer is particularly desirable when the chemical processing involves gas reactants which easily migrate to all exposed surfaces of the wafer being processed.
Limiting the activity of processing chemicals is also desirable to reduce the quantity of chemicals which are consumed. Unnecessarily processing the back surface of a wafer consumes increased chemicals. Processing unnecessary surfaces also increases the quantities of residual or spent chemicals which are costly to treat or cause a disposal problem.
In one semiconductor process in particular it is desirable to prevent back face processing from occurring during at least one of the processing steps. This particular process is in the context of preparing semiconductor substrates for epitaxial layer growth. Formation of the epitaxial layers is susceptible to contamination from minute amounts of materials which can emanate from the back face of the substrate upon which the epitaxial layer is being formed.
In preparing the substrate for growth of the epitaxial layer it is necessary to remove all pre-existing oxide from the surface on which the epitaxial layer is being developed. This is typically done by etching with aqueous hydrogen fluoride or vaporous aqueous hydrogen fluoride. In the past, the back side of the wafer has been protected by a polymer layer. The polymer layer required additional processing to remove the layer before epitaxial development is performed. The current invention addresses this need by allowing oxide to be removed from the face of the substrate, while allowing the native or other oxide layer on the back side of the substrate to be maintained. This reduces the risk that diffusion may occur from the back of the substrate which can lead to undesired materials being incorporated into the epitaxial layer.
In other processes it is a requirement that particular coatings or reactants not contact one side of a wafer because of contamination effects which result in subsequent processing.
Thus there is a need for improved techniques which limit semiconductor processing to protect a surface or surfaces against chemical exposure otherwise desired upon one or more other surfaces of the wafer or other semiconductor piece being processed. In the past there have not been adequate semiconductor wafer processing equipment which can provide acceptable wafer face protection, particularly when the processing involves controlled rotational motion of the wafer while in the processing chamber.